1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the present invention is related to optical wavelength multiplexing or add/drop devices and the method for making the same in compact size, where the size of the device is small enough to fit in small form-factor optical modules, such as C Form-factor Hot Pluggable 4 (CFP4) and Quad Small Form-Factor Pluggable 28 (QSFP-28) for client-side data communication.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. Wavelength division multiplexing (WDM) is an exemplary technology that puts data from different sources together on an optical fiber with each signal carried at the same time on its own separate light wavelength. Using the WDM system, up to 80 (and perhaps more) separate wavelengths or channels of data can be multiplexed into a light stream transmitted on a single optical fiber. To take the benefits and advantages offered by the WDM system, there require many sophisticated optical network elements.
Optical add/drop and multiplexer/demultiplexer devices are those elements often used in optical systems and networks. For example, an exchanging of data signals involves the exchanging of matching wavelengths from two different sources within an optical network. In other words, an add/drop device can be advantageously used for the multi-channel signal for dropping a wavelength while simultaneously adding a channel with a matching wavelength at the same network node. Likewise, for transmission through a single fiber, a plurality of channel signals are combined via a multiplexer to be a multiplexed signal that is eventually separated or demultiplexed via a demultiplexer.
A typical prior art free-space WDM Demux, as disclosed in U.S. Pat. No. 8,537,468, is duplicated in FIG. 1. The device allows a multiple wavelength light traveling from a common port and to be separated into multiple narrow spectral bands respectively directed to individual channels. At each of the multiple channels, a dielectric thin film filter transmits a selected wavelength band to a designated channel port and reflect all other wavelengths. FIG. 2 shows a typical optical transmission and reflection spectra of a single-channel band-pass filter that transmits λi and reflects wavelength from λ1 to λi−1 and λi+1 to λn. The reflected wavelength signals continue propagating to next channel ports, where an in-band signal is transmitted out and the out-band signals are reflected and continue propagating along the optical path. After multiple bounces in a zig-zag fashion as shown in FIG. 1, multiple channel signals are dropped. The device can also be used as a multiplexer (Mux) with the common port outputting all wavelengths multiplexed or added from the individual channels. The design has a number of advantages including low back-reflection, low loss and high reliability.
At the moment, 40 Gb/s or 100 Gb/s is achieved by using 4-channel WDM Mux/Demux that is widely adopted commercially in the CFP4 and QSFP28 packaging. To meet the exploring data consumption requirement and achieve higher data transmission data of 800 Gb/s, it is practical to double the number of channels from 4 to 8 or more. However, this change does not simply mean doubling the size of current 4-channel WDM. The design is, as matter of fact, very challenging. The most important issue that needs to be resolved is how to fit all the 8 channels Mux/Demux into the form factor of CFP4 or QSFP4 which has a very limited space inside. The CFP4 form factor is a CFP Multi-Source Agreement (MSA) defining an optical transceiver in the CFP4 form factor to support 40 Gbit/s and 100 Gbit/s interfaces for Ethernet, telecommunication and other applications. QSFP stands for Quad Small Form-factor Pluggable (QSFP) and is a compact hot-pluggable transceiver compact used for data communications applications. It interfaces networking hardware to a fiber optic cable. It is an industry format jointly developed and supported by many network component vendors, allowing data rates from 4×10 Gbit/s. The format specification is evolving to enable higher data rates.
The present application discloses the designs of 8-channel WDM devices that can fit into the form factor of CFP4 or QSFP4